SPN 677 FMI 5 is the Detroit DD Series diagnostic fault code that identifies Engine starter relay open circuit. This DiagTechPro reference summarizes the official 1-page Detroit diagnostic sheet so a technician can confirm the condition before opening the truck, and it links to the full downloadable PDF.
Official document details
| Brand | Detroit |
| Model coverage | Detroit DD Series (EPA 2007-Current) diesel engines |
| System / Group | DD Series (EPA 2007-Current) / DTCs |
| Fault condition | Engine starter relay open circuit |
| Published source | TruckFaultCodes.com, Copyright © 2017 |
| Pages | 1 |
| File size | 0.2 MB |
| Format | |
| Language | English |
SPN 677 FMI 5 diagnostic overview
This Detroit sheet covers an engine starter relay open circuit. The technician disconnects the Motor Control Module (MCM) 21-pin connector, removes the engine starter relay, and measures the resistance between pin 21 of the MCM 21-pin connector and the relay, referring to the OEM wiring for the correct pin location. If the resistance is greater than 1K ohms the wire between pin 21 and the relay is repaired; otherwise the engine starter relay is replaced per OEM procedures.
Document table of contents
- Fault code identification
- MCM 21-pin resistance measurement
- OEM pin-location note
- Wire repair or relay replacement
Applicable truck models covered
This diagnostic applies to Detroit DD Series (EPA 2007-Current) diesel engines across all model years, and is also grouped under the Series 60 (DDEC VI – EPA 2007) DTCs. It covers an open circuit on the engine starter relay wiring at the Motor Control Module 21-pin connector. For the OEM wiring schematics referenced in this procedure, see the official Detroit engine manufacturer site.
Who needs the SPN 677 FMI 5 manual
Workshop technicians and fleet owners using the diesel diagnostic tool to read Detroit fault codes and test the engine starter relay and Motor Control Module wiring will need this sheet. The full step-by-step PDF is available in the DiagTechPro manuals library, and a free account is required to download it.
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